1. Field of the Invention
This invention relates to an exhaust hood for removing air laden with grease, smoke or other contaminants from a working environment, and more specifically to such an exhaust hood with mechanisms for adjusting the volume of air passing through the hood and generating an air curtain beneath the hood.
2. Description of Related Art
Exhaust hoods are used in a variety of environments such as kitchens, laboratories and factories for exhausting heated or contaminated air from a working environment. In a restaurant kitchen, for example, there are usually a number of cooking units aligned in a row. Some of these units, broilers and fryers for example, may produce considerable quantities of smoke, fumes, grease particles and moisture, while other units such as ranges and griddles may generate such pollutants in considerably smaller amounts. Kitchen exhaust ventilators have traditionally been designed with enough airflow capacity to remove pollutants from broilers, fryers and other more active pollution-generating cooking units. This results in excessive ventilation for those cooking units which generate less pollution, such as the ranges and griddles.
A typical exhaust hood comprises a housing in the form of a box-like structure with an intake comprising an open underside, and an exhaust duct leading outwardly from its upper side. Air from the kitchen environment passes into the housing through a series of grease filters, and into an exhaust plenum above the grease filters. From the exhaust plenum, it is drawn out of the hood through the exhaust duct. In a kitchen the hoods are typically horizontally elongated to accommodate a row of cooking units.
An elongated hood may give rise to uneven distribution of air across the width of the hood. The portion of the hood directly beneath the exhaust duct tends to remove air at the greatest volume-rate, while portions of the hood displaced from the exhaust duct tend to exhaust air at lower volume-rates. A common solution to this problem is to situate the most active of the pollution-generating cooking units directly beneath the exhaust duct and to place the least active pollution-generating units furthest from the exhaust duct. However, such an arrangement may not promote optimal efficiency of the cooks working at the equipment, and many chefs prefer to experiment with different equipment locations to achieve maximum efficiency within the kitchen
To improve the flow distribution across a given exhaust hood, prior designs have incorporated a flow restriction strategically located in the path of the exhaust air to provide a desired flow distribution. For example, U.S. Pat. No. 4,281,635, issued Aug. 4, 1981 to E. C. Gaylord, discloses a kitchen ventilator or exhaust hood mounted over an arrangement of kitchen equipment which includes a broiler, a fryer, a range and a griddle. Air and grease pass from the equipment through an inlet opening and take a circuitous path through a series of opposing horizontal baffles to extract grease and other contaminants. A damper baffle mounted on a horizontal pivot at the inlet opening is pivotable toward and away from the lowest baffle to vary the width of a gap between the damper and the baffle, whereby to vary the volume of air flowing past the damper. To accommodate the varying exhaust requirements of different pieces of kitchen equipment, additional baffling is provided to reduce the rate of air flow into portions of the ventilator positioned above the range and griddle units. The additional baffling comprises choke plates attached to the hood in strategic locations and extending into the path of the exhaust air passing through the grease baffles. Several of the choke plates are bolted in place and others are spot-welded in place. To rearrange equipment beneath the exhaust hood, the choke plates must be removed and repositioned. To remove those choke plates which are spot-welded, the welds must be burned off
The volume of air exhausted through the hood must be replenished from some source. If exterior air is drawn into the kitchen area, it is typically tempered, particularly in northern climes. Such systems require additional energy expenditures. It is also known to draw air (often called "make-up" air) from adjacent rooms in restaurants, for example, but such systems require additional ducting and sometimes result in uneven air distribution from room to room.
Sometimes air curtains are generated across the front of a hood to "seal" smoke and grease-laden air beneath the hood and prevent it from entering the kitchen area. Many such air curtains are generated by structure mounted to the front of a hood and obtain source air from the exterior of a building, or from make-up air. Both sources require costly installations of extra ductwork.